调用EJB时​​出现Nullpointer异常

Question

以下代码似乎在NullPointerException类中抛出QuestionRepository，但我无法修复它。我不知道我是否对上下文依赖注入做了任何错误？

实体

@Entity
@NamedQueries({
    @NamedQuery(name=Question.ALL, query="SELECT q FROM Question q")
})
public class Question implements Serializable {

    private static final long serialVersionUID = 2402027045394206281L;

    public static final String ALL = "Question.all";

存储库

@Named
public class QuestionRepository {

    @PersistenceContext(unitName="SertifikatPU")
    private EntityManager entityManager;

    public List<Question> all() {
        TypedQuery<Question> query = entityManager.createNamedQuery(Question.ALL, Question.class);
        return query.getResultList();
    }
}

EJB

@Local(QuestionLocal.class)
@Stateless
public class QuestionServiceBean implements QuestionLocal {

    @Inject
    private QuestionRepository questionRepository;

    @Override
    public List<Question> findAllQuestions() {
        return questionRepository.all();
    }
}

支持bean

@ManagedBean
@ViewScoped
public class QuestionIndexBean implements Serializable {

    private static final long serialVersionUID = 4228471944163051591L;

    @Inject
    private QuestionLocal questionBean;

    private List<Question> questions;

    public void init() {
        setQuestions(questionBean.findAllQuestions());
    }

    public List<Question> getQuestions() {
        return questions;
    }

    public void setQuestions(List<Question> questions) {
        this.questions = questions;
    }
}

例外：

WARNING: A system exception occurred during an invocation on EJB QuestionServiceBean method public java.util.List com.mycompany.application.QuestionServiceBean.findAllQuestions()
javax.ejb.EJBException
    at com.sun.ejb.containers.BaseContainer.processSystemException(BaseContainer.java:5193)
    at com.sun.ejb.containers.BaseContainer.completeNewTx(BaseContainer.java:5091)
    at com.sun.ejb.containers.BaseContainer.postInvokeTx(BaseContainer.java:4879)
    at com.sun.ejb.containers.BaseContainer.postInvoke(BaseContainer.java:2039)
    at com.sun.ejb.containers.BaseContainer.postInvoke(BaseContainer.java:1990)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:222)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
    at $Proxy208.findAllQuestions(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.jboss.weld.util.reflection.SecureReflections$13.work(SecureReflections.java:305)
    at org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:54)
    at org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInvocation(SecureReflectionAccess.java:163)
    at org.jboss.weld.util.reflection.SecureReflections.invoke(SecureReflections.java:299)
    at org.jboss.weld.bean.proxy.EnterpriseBeanProxyMethodHandler.invoke(EnterpriseBeanProxyMethodHandler.java:125)
    at org.jboss.weld.bean.proxy.EnterpriseTargetBeanInstance.invoke(EnterpriseTargetBeanInstance.java:62)
    at org.jboss.weld.bean.proxy.ProxyMethodHandler.invoke(ProxyMethodHandler.java:125)
    at com.mycompany.application.org$jboss$weld$bean-SertifikatEJB_jar-SessionBean-QuestionServiceBean_$$_WeldProxy.findAllQuestions(org$jboss$weld$bean-SertifikatEJB_jar-SessionBean-QuestionServiceBean_$$_WeldProxy.java)
    at com.mycompany.web.QuestionIndexBean.init(QuestionIndexBean.java:25)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.sun.el.parser.AstValue.invoke(AstValue.java:234)
    at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297)
    at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:43)
    at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:56)
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
    at com.sun.faces.facelets.tag.jsf.core.DeclarativeSystemEventListener.processEvent(EventHandler.java:128)
    at javax.faces.component.UIComponent$ComponentSystemEventListenerAdapter.processEvent(UIComponent.java:2508)
    at javax.faces.event.SystemEvent.processListener(SystemEvent.java:106)
    at com.sun.faces.application.ApplicationImpl.processListeners(ApplicationImpl.java:2129)
    at com.sun.faces.application.ApplicationImpl.invokeComponentListenersFor(ApplicationImpl.java:2077)
    at com.sun.faces.application.ApplicationImpl.publishEvent(ApplicationImpl.java:286)
    at com.sun.faces.application.ApplicationImpl.publishEvent(ApplicationImpl.java:244)
    at javax.faces.application.ApplicationWrapper.publishEvent(ApplicationWrapper.java:670)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:108)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:330)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
    at com.mycompany.repository.QuestionRepository.all(QuestionRepository.java:17)
    at com.mycompany.application.QuestionServiceBean.findAllQuestions(QuestionServiceBean.java:21)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1052)
    at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1124)
    at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:5366)
    at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:619)
    at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
    at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:571)
    at org.jboss.weld.ejb.SessionBeanInterceptor.aroundInvoke(SessionBeanInterceptor.java:46)
    at sun.reflect.GeneratedMethodAccessor109.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:861)
    at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
    at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:571)
    at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doAround(SystemInterceptorProxy.java:162)
    at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:144)
    at sun.reflect.GeneratedMethodAccessor108.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:861)
    at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
    at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:370)
    at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:5338)
    at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:5326)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:214)
    ... 61 more

持久性XML

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
    <persistence-unit name="SertifikatPU">
        <jta-data-source>jdbc/sertifikat</jta-data-source>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
    </persistence-unit>
</persistence>

项目结构：

Answer 1

尝试将项目合并为一个。当使用多个项目时，框架中可能存在错误。

Answer 2

您的问题位于您的班级QuestionRepository。

如果我读得对，这是一个简单的类，而不是服务器托管类。这是什么意思？这意味着由于这个原因，这段代码

@PersistenceContext(unitName="SertifikatPU")
    private EntityManager entityManager;

什么都不做，因为类是由您实现的，也不是由服务器实例化的，因此从类的角度来看，持久化上下文是未知的。结果是在另一段代码中

public List<Question> all() {
        TypedQuery<Question> query = entityManager.createNamedQuery(Question.ALL, Question.class);
        return query.getResultList();
    }

entityManager将为null，因此会导致空指针异常。

解决方案？例如，将QuestionRepository声明为EJB。这样，持久性上下文注入将由服务器自动完成，并且在您尝试执行查询时将初始化实体管理器